1. Field of the Invention
The present invention relates to an electrothermal converting element board provided with an electrothermal converting element having a plurality of heat generating sections arranged in correspondence to liquid flowing paths for guiding liquid used for the printing, an ink jet printing head provided with the electrothermal converting element board and an ink jet printing apparatus using the same.
2. Description of the Related Art
An ink jet printing apparatus generally has a printing head for ejecting ink used as a printing liquid. A bubble-jet (a registered trade mark) type printing head includes an ink ejection member having an ink ejection opening forming surface on which a plurality of ink ejection openings for ejecting ink droplets are formed at a predetermined distance, an electrothermal converting element board on which electrothermal converting elements are arranged in correspondence to each ink flow path in communication with the respective ink ejection opening in the ink ejection member, and a printed wiring board for supplying drive control signals to the respective electrothermal converting elements in the electrothermal converting element board (see. for example, Japanese Patent Application Publication No. 62-048585 (1987))
The ink ejection member has a common liquid chamber for storing a predetermined amount of ink supplied from an ink tank. The common liquid chamber communicates with one ends of the respective ink flow paths formed by opposite partitioning wall members arranged in parallel to each other. Thereby, ink is distributed from the common liquid chamber to the respective ink flow paths and ejected through the ink ejection opening as ink droplets.
As shown, for example, in FIGS. 7A and 7B, the electrothermal converting element board includes a base 6 disposed between a portion in which the ink flow paths of the ink ejection member are formed and the printed wiring board, and provided on one surface thereof closer to the ink flow paths with a heat generating section 8ai (i=1 to n; n is an integer) of a heater used as the electrothermal converting element and a heat generating section 20ai (i=1 to n; n is an integer) in correspondence to the respective ink flow path; an individual electrode layer 10 electrically connected at one end to the heat generating section 8ai; an individual electrode layer 18 arranged in the same plane as the individual electrode layer 10 and electrically connected at one end to the heat generating section 20ai; a common electrode layer 12 formed in the same plane as the individual electrode layers 10 and 18 and electrically connected at one end to the heat generating section 8a i and the heat generating section 20ai, respectively; a protective layer 16 for covering all the heat generating section 8ai, the heat generating section 20ai, the individual electrode layer 10 and the individual electrode layer 18 adjacent to each other; and an anti-cavitation layer 14 for covering all over the surface of the protective layer 16.
In this regard, in FIGS. 7A and 7B, part corresponding to two of all ink flow paths 2ai (i=1 to n; n is an integer) of the ink ejection member is solely illustrated as a representative and the other is omitted.
The heat generating section 8ai and the heat generating section 20ai are arranged on a common straight line along the ink flow path in the same plane as the base 6. The heat generating section 8ai is located at a position closer to the ink ejection opening of the ink ejection member than the position of the heat generating section 20ai. A capacity (a heat value) of the heat generating section 8ai is less than the capacity (a heat value) of the heat generating section 20ai.
To the other end of the common electrode layer 12 formed on the heat generating section 8ai, 20ai, a reference electric power source for supplying a predetermined electric power is connected.
The anti-cavitation layer 14 having undulations on a surface thereof has a shallow groove between the adjacent partitioning wall members 4ai (i=1 to n; n is an integer) of the ink ejection member and an elongate groove 14a in correspondence to the respective partitioning wall member 4ai. In this regard, the number of the ink ejection openings is recently liable to increase due to the requirement for the high resolution of the resultant printed image. Accordingly, a mutual distance between the adjacent heat generating sections 8ai and 20ai becomes relatively smaller.
One end of the partitioning wall member 4ai in the ink ejection member is brought into tight contact with the anti-cavitation layer 14 at a predetermined pressure so that the adjacent ink flow paths 2ai thus formed are independent from each other without communication. When a plurality of pairs of heat generating sections 8ai and 20a are formed in the respective ink flow paths and the individual electrode layers 10 and 18 and the common electrode layer 12 are arranged parallel to each other in the same plane as described above, wirings and routes of the wiring are relatively increased and complicated between the respective electrode layers and the reference electric power source.
Also, when the number of the ink ejection openings is increased, with the trend moving toward greater densities, it might be thought to reduce a width of the respective heaters and that of the individual electrode layers 10, 18 and the common electrode layer 12 so that a width of the respective ink flow path is narrower. There is a risk, however, if the width of the respective heater becomes narrower, in that the ink ejection reduces in performance as the heating efficiency becomes lower. Also, the reduction of the width of the individual electrode layers 10, 18 and the common electrode layer 12 has a limitation because the wiring resistance becomes larger. Accordingly, it is difficult to realize the greater-density of the heat generating sections in the electrothermal converting element board and the ink ejection openings as well as to miniaturize the electrothermal converting element board.